Method of drying photographic material



Patented Mar. 4, 1952 STATES PATENT OFFICE METHOD F DRYING PHOTOGRAPHIC MATERIAL.

Cornelis Johannes Dippel, Jan Anthonyfl'iely; and" Johannes Aloysius Maria.` Dikhoft', Eindhoven, Netherlands, assignors to. Hartford; National Bank and Trust Companyg, Hartford,` Gonn., as4

trustee Application May 19, 19471Seria'l'No. 148;974 In the Netherlands June 1, 1946 4 Claims.

drying operationcan be effected in a very simple manner. This is yof importa-nce with a view to the `manufacture `of copying material for image lms, sound. films, and combined image-andsound films.

The invention has `for its object a further simplifl'cation of the manufacture; It permits the drying. process to be reiected very rapidly by meansv of lapparatus which `occupy only little space. It is `:known to effect the :sensitisation rapidly `and by means of compact apparatus, the speed of manufacture of vthe said `photographic material: and the sizeof the apparatus required therefor Vbeing fundamentally determined by the rateuof drying. and the size of the drying chamber.` By making use of the invention, it is pos- 'sible tocarry out the Whole process rapidly and by .means vof apparatus occupying little space.

`According to the invention the :sensitized material .is dried rby heating .it a high frequency electric-field. `While passing a-stream of gas over the photographie' material in order to carryA away any evolved Water vapour, .the material lis treated in an electric 'field having such "a frequency land fstrengththat, on 4an average, atleast 15 percent. by `volume of water lis expelled per second.v This means that ineach cubic centi'metre of the material 'an energy of `at least about 80 calories `l`per second is produced. Avalue of l5 percent. by volume fof wateris to be understood to mean 15 ccs Aof Awater per 100 lcc.s of dry material.

If a heating method according to the invention is used for a lm strip consisting of regenerated cellulose having a thickness of 40 u, which fcontains- 5 mgs. of water per sq. c. of its surface after sensitisa'tion, itis possible to dry the fllm istrip in approximately 6 seconds. If the lm strip :is passed fthrough yan electric lrleld which extends over a length of 1.45 cms., the `speed may .consequently be 'about 45 ms. `per minute. According to the invention, it is even possible to 'raise the speed `of .drying toa degree .such that `3.0 percent. b y volume :of Water Vis `expelled per second.y

.It .is surprising that it `has been `found to be possible to heat the photographic material to such ahigh .degree without jgeopardizing, the sensitized compound, which. is very remarkable, since. light.- sensitive'` nitrogen compounds; such as i diazonium compounds.. aziclesy `and the4 like, readily decom- `poseen being heated; and would disintegratefor theA greater part at.V such an intensive heat. sunfply inf` a drying chamber operated, for example, by means of hot air. Furthermore it. shouldihe considered that, according to the .inyention, ,l1eat is developed within the material.. solthatz the ,infterior of the material is-warmer than. itscsurface. In the .case of external heating, .for example by means of hot air, the interior .of thematerial is `colder than the heating medium.

Decomposition Aof 'the lightfsensitive compound "may cause a dense fog, `particularly. in `the .case

`of `light-sensitive material `in which the light;-

decomposition product. of the light-sensitive com.- pou-nd forms metal nuclei out of the metalsalts contained i-nthe material, which `nuclei are amplifled upon subsequent physical development.` `.An example `thereof 'is a material which is sensitized by means of 1a solution of a diazonium compound and a mercury salt ora precious metal salt. When heating according to the invention, however, this `material does not involve any fog at all.

The photographic material is preferably .heated by means of an `electric field generated between wireory rod-shaped electrodeswhich extend parallel with the surface of the material and in front of which the material is passed in a Imanner 'such that the lines of force of the `field `extend substantially in this direction of motion through the material. If desired, the electrodes may be moved, rwhereas the `material is stationary. With such an electrode arrangement the lines of force extend Aover a comparatively large `distance through `the material itself `and over a comparatively short distance `only through the medium,

for example, yair `between the electrodes and `the material. Thelefciency `of the field is `thus fenhanced, which is conducive tothe compactness 'of the apparatus.

Though in the .case ofthe electrode arrangement referred to the eld strength in the direction of motion of the material is not constant. the results of the treatment in this direction `are homogeneous, if only the motion .takes place at a constant speed. The homogeneity in a lateral direction Vof the material is controllable by using electrodes `the length of which `exceeds.. of the material.

The quantity `of for example air, which :is passed over the Vnraterial to carry awayv any .ex-

pelled water vapounis preferably so chosen that it is exactly sumcient to absorb the evolved water vapour without becoming supersaturated. The excess air may, for example, be 100% or less. This'` has the advantage that the possibility of dust'fparticles of the air contaminating the photographic material is reduced as much as possible. Useffis preferably made of a gas which is preheated to approximately 50 C. and is consequently capable of absorbing a large quantity of water vapour.

The invention is of much importance for photographic material in which the quality of the photographic contrast depends upon the moisture content of the material at the moment of exposure. An example of such a material is regenerated cellulose which is sensitized by means of an aqueous solution of a diazonium compound anda mercury salt or a noble metal salt. exposing such a material, followed by physical development, it is found that the gamma value of the metal image obtained depends upon the moisture content at the moment of exposure A(cfjapplication Serial No. 727,310, filed February 8, 1947, now Patent No. 2,571,671 and application Serial No. 723,426, filed January 21, 1947, now Patent No. 2,571,670). The exposure of such a material, for example for the manufacture of copies of image-and-sound films is preferably effected in a device comprising an apparatus for applying liquid water on to the material, a drying chamber for the adjustment of the degree of humidity of the material, exposure apparatus and. means for passing the material through these members in succession (application Serial No. 732,904, filed March 6, 1947, now abandoned). In vv'such a device use may, if desired, be made of unsensitized material, the water and the lightsensitive. compound then going into solution therein being applied simultaneously. By effecting-the drying operation in such a device in the manner according to the invention, an appreciable simplification of the apparatus is ensured. Thijs is particularly the case if the high-frequency drying operation is effected by means of the aforesaid electrode arrangement. Thus a device is obtained which has practically the same size as a cbpying device in which the operations preceding the exposure are not effected. Furthermore the said electrode arrangement yields a material having a high degree of homogeneity. This is ofimportance, since local differences in moislture content give rise to different gamma values.

Onv drying by means of heated air there is a risk ofjthe edge of the material having a different Vmoisture content from that of the central part. v

Aj further very important advantage of highfrequency drying in this case is that, owing to thespeed of drying and consequently the speed Aat which the desired degree of. humidity can be adjusted, one and the same film band permits changing over from one degree of humidity to `the, other in a short time. This may be ofim- 'portance if, -for example, it is desired to fcopy on one and the same nlm strip several scenes -in succession with different gamma values, for

The invention will be described in connection with the accompanying drawing in which:

Fig. 1 shows one form of apparatus for drying -iilm according to` the invention; and' shows another form of apparatus for lji) drying film according to the invention. The wet film I passes between electrodes 2 of a highfrequency field arranged in a drying chamber 3 provided with an air intake inlet 4 and an air outlet 5. The electrodes are excited by a high frequency lgenerator 6 connected to the electrodes by conductors 'I which are insulated from Ithe walls of the chamber by insulators 8. In Fig. 2, the electrodes 2 of the high frequency drying field are so arranged with respect to the film that the lines of force 9 of the field pass through the film in its direction of motion as indicated by the arrow.

While the invention has thus been described in" connection with specic embodiments and applications thereof, other modifications therein' will be obvious to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. A method of drying a photographic film hav- `ing a thickness of about 40 microns comprising a,

carrier of regenerated cellulose sensitized with an aqueous solution ofalight sensitive diazonium compound and a salt of a noble metal, said photographic film containing at leastv 1.4 grams of water per cubic centimeter of dry cellulose, comprising the steps of subjecting the photographic vfilm to the action of an electric field of a strength and frequency at which calories per second are generated in the film and capable of expelling more than three-fourths of theinitial water content of said film within ive seconds, and passing a stream of dry gas over said photographic lm during the expulsion of water therefrom to carry the expelled water off as water vapor.

2. A method of drying a photographic iilm having a thickness of about 40 microns comprising a carrier of regenerated cellulose sensitized with an aqueous solution of a light sensitive diazonium :compound and a salt of mercury, said photographic film containing at leastv 1.4 grams of vwater per cubic centimeter of .dry cellulose, .com-

prising the steps of subjecting the photographic film to the action of an electric field of a strength and frequency at which 80 calories per second Vare generated in the film and capable of expelling more than three-fourths of the initial water content of said lm within iive seconds, and passing a stream of dry gas over said photographic film during the expulsion of water therefrom to carry the expelled water ofi as water vapor.

3. A method of drying a photographic carrier having a thickness of about 40 micronsv comprising a carrier of regenerated cellulose sensitized with an aqueous solution of a light-sensitive diazonium compound and Va salt of a metal lying higher in the electromotive series than copper, -said photographic film containing at least 1.4

grams of water per cubic centimeter of dry cellulose, comprising the steps of subjecting the photographic film to the action of an electric field .of a strength and frequency at which 80 calories per second are generated in the film and capable of expelling at least 15% by volume of the water in said carrier per second, andpassing a stream of dry gas over said photographic iilm during the expulsion of water therefrom to carry the expelled water off as Water vapor.

4. A method of drying a photographic carrier having a thickness of about 40 microns comprising a carrier of regenerated cellulose sensitized with an aqueous solution of a light sensitive diazonium compound and a salt of a metal lying higher in the electromotive series than copper,

said photographic film containing at least 1.4 grams of water per cubic centimeter of dry cellulose, comprising the steps of subjecting the photographic film while in motion to the action of an electric field in which the lines of force of the eld extend through the lm substantially in the direction of motion of the film, said iielcl having an intensity and frequency at which 80 calories per second are generated in the lm and which is capable of expelling at least 15% by volume of water per second in the lm, and passing a stream of dry gas over said photographic carrier during the expulsion of Water therefrom to carry the expelled water off as Water vapor.

CORNELIS JOHANNES DIPPEL. JAN ANTHONY LELY. JOHANNES ALOYSIUS MARIA DIKHOFF.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,997,507 Akintievsky Apr. 9, 1935 2,042,145 Darrah May 26, 1936 2,106,868 De Boer et al Feb. 1, 1938 2,183,447 Dippel et al Dec. 12, 1939 2,226,871 Nicholas Dec, 31, 1940 2,231,457 Stephen Feb. 11, 1941 2,291,807 Hart, Jr Aug. 4, 1942 2,459,622 Cohoe et al Jan. 18, 1949 FOREIGN PATENTS Number Country Date 735,718 i France Sept. 6, 1932 853,868 France Dec. 16, 1939 

1. A METHOD OF DRYING A PHOTOGRAPHIC FILM HAVING A THICKNESS OF ABOUT 40 MICRONS COMPRISING A CARRIER OF REGENERATED CELLULOSE SENSITIZED WITH AN AQUEOUS SOLUTION OF A LIGHT SENSITIVE DIAZONIUM COMPOUND AND A SALT OF A NOBLE METAL, SAID PHOTOGRAPHIC FILM CONTAINING AT LEAST 1.4 GRAMS OF WATER PER CUBIC CENTIMETER OF DRY CELLULOSE, COMPRISING THE STEPS OF SUBJECTING THE PHOTOGRAPHIC FILM TO THE ACTION OF AN ELECTRIC FIELD OF A STRENGTH AND FREQUENCY AT WHICH 80 CALORIES PER SECOND ARE GENERATED IN THE FILM AND CAPABLE OF EXPELLING 